This invention relates to electric power cables and a method of making same.
Certain techniques are already known for manufacturing electric power cables with cured polyethylene as the insulating material. According to one general operation, a mixture of curable polyethylene and a curing agent extruded to cover the surfaces of an electric conductor is cured by saturated steam and subsequently subjected to cooling by water. Saturated steam as the heating medium in this operation is used by virtue of its low degree of laminar film resistance, good thermal conductivity and great heat capcity as well as its moderate price and ready availablity.
The above prior art technique is disadvantageous due to the invasion of steam into the polyethylene insulating material during the curing process, which forms many watery areas, or the so called cloudy zones having micro-voids which will inevitably cause the cured polyethylene layer to lose its insulation properties. Such a disadvantage has, of late years, proved to be more and more critical due to the recently increasing need for high-voltage power transmission cables.